Perhaps this has already been posted but now the challenge is coming to an end so I think it's worth posting. This challenge was created by Samsung to spur apps that make use of the S Pen, they don't have to be exclusive to the Note, but they must make use of its SDK and such things. The prizes are quite cool with $100.000 going to the winner (the results will be announced tomorrow). Among the competing apps there is a lot of garbage, but there are also a few gems.
I recommended Jotter in other post I did. Well, I take that back. Jotter is five bucks and it's actually worse than Papyrus, which is free.
Papyrus is a note-taking app (I know, yawn) that makes the S Pen actually enjoyable. It's hard to explain, but basically the S Pen works A LOT better than in any other app. It does show real pressure sensitivity, and it's super-smooth and accurate. And you can rest your hand on the screen, too. The interface is pure joy, and by looking at the developer it's clear that they want to make something bigger than "another note-taking app".
Also: artistic types seem to love Infinite Painter, which is free (and will probably become paid in a couple of days, since I suspect it was only free for the app challenge). I don't draw much and frankly I uninstalled it after trying it a bit, but well, I had to tell you.
Other than that, there's an app for PDF signing called Significant that works very well but....to be honest, I sign about 1 PDF per year. By contrast, I use Papyrus every day. There's also a cloud-collaboration thing called Soonr Scribble (available on Google Play, not in the challenge) and lets mark up and annotate Office files, but I already keep my stuff in Google Docs so I didn't see the point.